EP0565267B1 - Dispositif de blindage pour tube à rayons cathodiques - Google Patents

Dispositif de blindage pour tube à rayons cathodiques Download PDF

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Publication number
EP0565267B1
EP0565267B1 EP93302219A EP93302219A EP0565267B1 EP 0565267 B1 EP0565267 B1 EP 0565267B1 EP 93302219 A EP93302219 A EP 93302219A EP 93302219 A EP93302219 A EP 93302219A EP 0565267 B1 EP0565267 B1 EP 0565267B1
Authority
EP
European Patent Office
Prior art keywords
envelope
conductive
tracks
crt
guard screen
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP93302219A
Other languages
German (de)
English (en)
Other versions
EP0565267A1 (fr
Inventor
David Richard Birchall
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Fujitsu Services Ltd
Original Assignee
Fujitsu Services Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Fujitsu Services Ltd filed Critical Fujitsu Services Ltd
Publication of EP0565267A1 publication Critical patent/EP0565267A1/fr
Application granted granted Critical
Publication of EP0565267B1 publication Critical patent/EP0565267B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
    • H01J29/06—Screens for shielding; Masks interposed in the electron stream

Definitions

  • This invention relates to cathode ray tubes (CRTs) according to the first part of claim 1.
  • the invention is particularly, although not exclusively, concerned with CRTs for use in monitors and display terminals for data processing apparatus.
  • Electric field emissions from a CRT comprise both DC and AC components.
  • the DC electric field generated on the surface of a CRT screen is relatively easy to reduce to acceptable levels by the incorporation of a conductive coating, available from all tube manufactures.
  • a conductive coating available from all tube manufactures.
  • 'normal' conductive coatings are high resistance and cannot cope with high levels of AC field.
  • Very low Ohmic coatings or screens are available but at high cost.
  • FR-A- 2 379 906 describes a CRT with a guard screen according to the first part of claim 1, comprising a continuous conductive layer on the outside of the CRT envelope.
  • the guard screen extends between a deflection yoke and an internal conductive layer. Such a guard layer would reduce the capacitive coupling between the deflection yoke and the internal conductive layer.
  • forming the guard screen as a continuous layer allows eddy currents to be induced in the layer by the deflection yoke, thus giving rise to heat generation.
  • US-A- 4 392 083 describes a radiation shield for the neck of a CRT.
  • the shield consists of a cylindrical sleeve which fits over the neck of the CRT envelope.
  • the sleeve is formed of thin insulating material with a pattern of parallel conductors on its inner and outer surfaces, the conductors on the two surfaces being offset so as to provide a continuous covering around the sleeve.
  • Such a sleeve is easy to fit on the CRT and reduces the eddy current problem.
  • such a cylindrical sleeve can only be used around the neck of the CRT, and is not suitable for use around the flared portion, to provide a screen between the deflection yoke and the internal conductive layer.
  • the object of the invention is to provide a way of overcoming all the above problems.
  • CRT cathode ray tube
  • Figure 1 is a sectional elevational view of a CRT embodying the invention.
  • Figure 2 is a cross-sectional view showing the guard screen in more detail.
  • Figure 3 shows a typical conductive pattern on the guard screen.
  • the CRT comprises an evacuated glass envelope 10 having a cylindrical neck position 12, a flared portion 14 and a face 16.
  • An electron gun 18 is positioned in the neck 12 of the tube, and the face 16 is coated with a phosphor, in the conventional manner.
  • the envelope 10 has an internal aluminised layer 20 on its inner surface, extending from the end of the neck 12, up the flared portion 14, and over the screen 16.
  • the CRT has scan coils 22 positioned around the neck 12, for deflecting the electron beam from the electron gun 18.
  • a conductive guard screen 24 is positioned around the CRT, between the scan coils 22 and the envelope 10. This screen is connected, in use, to ground potential.
  • the guard screen 24 thus prevents or reduces the voltages induced between the coils 22 and the internal layer 20, and hence reduces AC emissions from the face 16 of the CRT. It has been found that a reduction in the order of 90-95% of the AC emissions can be achieved by use of the guard screen.
  • the guard screen 24 is formed from a flexible printed circuit, wrapped around the envelope 10.
  • the flexible printed circuit comprises a flexible insulating substrate 26, having first and second conductive patterns 28, 30 on opposite sides of the substrate.
  • the substrate 26 may comprise a polyimide film such as for example KAPTON®, having a thickness of 50 microns.
  • the substrate may comprise a KAPTON base with insulating coating layers, with a total thickness of 150 microns.
  • Each of the conductive patterns comprises a set of parallel fingers, the fingers of the two patterns being interdigitate so that, the fingers of one set are positioned over the gaps between the fingers of the other set. Thus, between them, the two sets of fingers provide complete screening, without any gaps.
  • this shows a typical conductive pattern on one side of the substrate.
  • the pattern on the other side is similar, but has its conductors offset to produce the interdigitated arrangement.
  • each pattern includes a set of parallel fingers 32, which, when the flexible printed circuit is wrapped around the CRT, form a cylindrical portion of the guard screen around the neck of the envelope.
  • Each pattern also includes two sets of concentric, arc-shaped fingers 34 which, when the guard screen is in position, form a conical portion, around the flare of the envelope.
  • the arc-shaped fingers may be replaced by radial fingers.
  • each finger preferably does not exceed approximately twice the line frequency AC signal penetration depth, otherwise the scan energy will be dissipated in heat generated from eddy current loss.
  • the maximum finger width lies in the range 0.5mm to 0.8mm.
  • the fingers do not have to be copper (ie standard PCB conductive coating), but could be formed in a conductive ink from a screen printing technique. Using this method a very thin, flexible guard screen could be manufactured in quantity and at competitive cost. The screen must be thin in order to fit between the scan coils and CRT neck, and flexible to form a cone around the CRT flare.
  • a further advantage of fitting a screen between the tube and scan coils is the improved immunity to the scan circuitry to tube 'flash over'. This occurs when the EHT in the tube final anode flashes across to other tube electrodes (a well known phenomenon). Capacitive coupling to the scan coils can cause failure of the electronic drive circuitry but with a screen fitted as described above, this problem would be vastly reduced.

Landscapes

  • Vessels, Lead-In Wires, Accessory Apparatuses For Cathode-Ray Tubes (AREA)
  • Electrodes For Cathode-Ray Tubes (AREA)

Claims (2)

  1. Tube cathodique (CRT) comprenant :
    une enveloppe (10) possédant une partie col (12) et une partie évasée (14);
    une couche d'anode conductrice interne (20) s'étendant sur l'intérieur de ladite partie évasée ;
    un bloc de déviation (22) entourant ladite enveloppe ; et
    un écran de garde conducteur (24) comprenant une partie cylindrique (32) qui entoure ladite partie col (12) et une partie évasée (34) qui entoure ladite partie évasée (14) de l'enveloppe, ledit écran de garde s'étendant entre ledit bloc de déviation (22) et ladite couche d'anode conductrice interne (20),
    caractérisé en ce que :
    ledit écran de garde conducteur (24) est formé à partir d'un circuit souple enroulé autour de l'extérieur de ladite enveloppe, ledit circuit souple comprenant un substrat isolant (26) doté d'une pluralité de pistes conductrices, lesdites pistes comprenant :
    un groupe de pistes conductrices initialement parallèles (32) qui, lorsque le circuit est enroulé autour de l'enveloppe, forment une partie cylindrique de l'écran de garde autour de ladite partie col de l'enveloppe, et
    au moins un groupe de pistes initialement concentriques, en forme d'arcs ou radialement disposées, (34) qui, lorsque le circuit est enroulé autour de l'enveloppe, forment une partie évasée de l'écran de garde autour de ladite partie évasée de l'enveloppe.
  2. Tube cathodique selon la revendication 1, où lesdites pistes conductrices sont disposées sur les deux côtés dudit substrat isolant (26), les pistes (28) qui se trouvent d'un côté du substrat étant en position interdigitée par rapport aux pistes (30) se trouvant sur l'autre côté du substrat.
EP93302219A 1992-04-07 1993-03-23 Dispositif de blindage pour tube à rayons cathodiques Expired - Lifetime EP0565267B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB929207543A GB9207543D0 (en) 1992-04-07 1992-04-07 Cathode ray tubes
GB9207543 1992-04-07

Publications (2)

Publication Number Publication Date
EP0565267A1 EP0565267A1 (fr) 1993-10-13
EP0565267B1 true EP0565267B1 (fr) 1996-01-03

Family

ID=10713564

Family Applications (1)

Application Number Title Priority Date Filing Date
EP93302219A Expired - Lifetime EP0565267B1 (fr) 1992-04-07 1993-03-23 Dispositif de blindage pour tube à rayons cathodiques

Country Status (7)

Country Link
EP (1) EP0565267B1 (fr)
JP (1) JPH0668807A (fr)
DE (1) DE69301177T2 (fr)
DK (1) DK0565267T3 (fr)
FI (1) FI931575A (fr)
GB (1) GB9207543D0 (fr)
NO (1) NO307397B1 (fr)

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2545120A (en) * 1948-02-27 1951-03-13 Rca Corp Cathode-ray tube arc-over preventive
NL7701287A (nl) * 1977-02-08 1978-08-10 Philips Nv Beeldweergeefinrichting.
US4392083A (en) * 1981-11-20 1983-07-05 Teletype Corporation Radiation shield for a cathode ray tube
GB2255441B (en) * 1991-04-18 1995-06-21 Mitsubishi Electric Corp Cathode-ray tube having alternating electric field reduction device

Also Published As

Publication number Publication date
EP0565267A1 (fr) 1993-10-13
NO931045D0 (no) 1993-03-23
NO307397B1 (no) 2000-03-27
JPH0668807A (ja) 1994-03-11
DK0565267T3 (da) 1996-02-05
DE69301177T2 (de) 1996-10-02
NO931045L (no) 1993-10-08
DE69301177D1 (de) 1996-02-15
FI931575A0 (fi) 1993-04-07
GB9207543D0 (en) 1992-05-20
FI931575A (fi) 1993-10-08

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